Evaluation of ground-motion characteristics for seismic hazard prediction

点击翻译按钮获取中文摘要

Strong-motion and microtremor observations are carried out in Kamakura and Kitahassaku area, Yokohama, in order to evaluate ground-motion characteristics in the areas. In Kamakura, four accelerographs are installed on soft rocks and Holocene lowland. The observed records contain siteamplification characteristics at each site although the records are contaminated by building vibrations. It is shown that the site-amplification characteristics can be detected by H/V spectral ratios of microtremors. The H/V spectral method is modified by introducing coherence between horizontal and vertical motions. The new method is applied to site-amplification evaluation in Kamakura. The results are consistent with the damage distribution in Kamakura area during the 1923 Kanto earthquake. In Kitahassaku area, three accelerographs are installed on loam plateau and Holocene lowland. Strong-motion observation shows that a plateau site has larger site-amplification characteristics in comparison to lowland sites by a factor of about 1.5 in peak horizontal ground velocity and about 2 in spectral peak amplitudes of Fourier amplitude-spectra. The amplification is due to subsurface soils which are accumulated on soft rocks. The site-amplification characteristics at the strong-motion sites can be detected by H/V spectral ratios of microtremors. Spot microtremor observations conducted in the area demonstrate that resonance periods on plateaus are related to elevation ; high site amplification areas distribute along rivers in the lowlands and the Shimosueyoshi plateau. The comparisons of spectral characteristics of strong motions and microtremors show the applicability of microtremors to evaluation of ground-motion characteristics for seismic hazard prediction.